1. Technical Field of the Invention
The present invention relates to cellular telephone networks and, in particular, to the handling of in-call service change requests.
2. Description of Related Art
The radio connection between a mobile station and the cellular telephone network, as well as the connections within the cellular telephone network itself, support both data communications and voice communications by subscribers. In particular, the connections support the use of a number of different types of data communications services and a number of different types of voice communications services. For example, on the data communications side both asynchronous data communication and Group 3 (G3) facsimile services may be supported. Furthermore, again for example, on the voice communications side both analog and digital speech services may be supported. A number of other types of voice and data communications services are known to those skilled in the art and are supported by the cellular telephone network.
It is not an uncommon occurrence for a cellular subscriber to need to make use of two or more of the various available communications services during the course of a single call connection. For example, the subscriber may be involved in a voice conversation with another party using one of the cellular network and mobile station supported voice services, and then need to send (or receive) a facsimile to (from) the other party. Many cellular telephone networks, such as the Personal Communications Services (PCS) network, digital Advanced Mobile Phone System (D-AMPS) network, and Global System for Mobile (GSM) Communications network, allow the subscriber to switch among and between a plurality of supported data and voice communications services without having to establish separate, and new, calls. This is accomplished through a known procedure referred to in the art as "in-call modification" or "in-call service change". By transmitting a certain signal over the radio connection to the currently serving switching node of the cellular network, a request for the service change is made. The serving switching node responds, again using a signaling transmission over the radio connection, with a reply granting or denying the service change. If the service change is granted, the serving switching node further takes the necessary steps to reconfigure the facilities of the cellular network (as and if required) to handle the newly requested and selected communications service.
The term "facilities" refers collectively to many types or classes of communications resources. For example, a switching node within a cellular telephone network uses both inter-switch and internal facilities. The inter-switch facilities comprise inter-switch circuits or trunks (both analog and digital) for handling call connections. The internal facilities comprise interworking functions (IWFs), trancoders for vocoding within the switch, radio related resources such as radio frequency channels (for communicating with mobile stations), and air interface bandwidth on a selected radio frequency channel. Responsive to a granted in-call service change request, it may become necessary for a switching node to modify existing facilities or allocate new facilities within the cellular telephone network to support the service change.
Consider now the situation where the subscriber has established a cellular call connection, and moves through the service area forcing an inter-exchange handoff of the call connection from a cell assigned to one switching node (the anchor switch) to a cell assigned to another switching node (the target switch, and then the serving switch after handoff). This handoff does not affect the continuation of the cellular call connection. It does, however, affect the ability of the cellular network to provide service changes and respond to in-call service change requests. This is because it is the anchor switching node which continues to exercise control over the cellular call connection, but it is the serving switching node which has received the service change request from the subscriber. There is a need for a system and method for insuring that service change requests, especially following instances of inter-exchange handoff, are routed through the cellular telephone network as needed to the proper switching node for handling and response.